Tylos was the name used by the Greeks to refer to Bahrain, as the centre of pearl trading, when Nearchus came to discover it serving under Alexander the Great.[1] From the 6th to 3rd century BC Bahrain was included in the Persian Empire by the Achaemenids, an Iranian dynasty.[2] The Greek admiral Nearchus is believed to have been the first of Alexander's commanders to visit the island, and he found a verdant land that was part of a wide trading network; he recorded: "That in the island of Tylos, situated in the Persian Gulf, are large plantations of cotton tree, from which are manufactured clothes called sindones, a very different degrees of value, some being costly, others less expensive. The use of these is not confined to India, but extends to Arabia."[3] The Greek historian, Theophrastus, states that much of the islands were covered in these cotton trees and that Tylos was famous for exporting walking canes engraved with emblems that were customarily carried in Babylon.[4]Ares was also worshipped by the country's indigenous and Greek population.[5]

It is not known whether Bahrain was part of the Seleucid Empire, although the archaeological site at Qalat Al Bahrain has been proposed as a Seleucid base in the Persian Gulf.[6] Alexander had planned to settle the eastern shores of the Persian Gulf with Greek colonists, and although it is not clear that this happened on the scale he envisaged, Tylos was very much part of the Hellenised world: the language of the upper classes was Greek (although Aramaic was in everyday use), while Zeus was worshipped in the form of the Arabian sun-god Shams.[7] Tylos even became the site of Greek athletic contests.[8]

The name Tylos is thought to be a Hellenisation of the Semitic Tilmun (from Dilmun).[9] The term Tylos was commonly used for the islands until Ptolemy’s Geographia when the inhabitants are referred to as 'Thilouanoi'.[10] Some place names in Bahrain go back to the Tylos era, for instance, the residential suburb of Arad in Muharraq, is believed to originate from "Arados", the ancient Greek name for Muharraq island.[11]

The Greek historian Strabo believed that the Phoenicians originated from Bahrain.[12]Herodotus also believed that the homeland of the Phoenicians was Bahrain.[13][14] This theory was accepted by the 19th-century German classicist Arnold Heeren who said that: "In the Greek geographers, for instance, we read of two islands, named Tyrus or Tylos, and Arad, Bahrain, which boasted that they were the mother country of the Phoenicians, and exhibited relics of Phoenician temples."[15] The people of Tyre in particular have long maintained Persian Gulf origins, and the similarity in the words "Tylos" and "Tyre" has been commented upon.[16] However, there is little evidence of occupation at all in Bahrain during the time when such migration had supposedly taken place.[17]

According to the Persians best informed in history, the Phoenicians began the quarrel. These people, who had formerly dwelt on the shores of the Erythraean Sea (the eastern coast of the Arabia peninsula), having migrated to the Mediterranean and settled in the parts which they now inhabit, began at once, they say, to adventure on long voyages, freighting their vessels with the wares of Egypt and Assyria...

— Herodotus

With the waning of Seleucid Greek power, Tylos was incorporated into Characene or Mesenian, the state founded in what today is Kuwait by Hyspaosines in 127BC. A building inscription found in Bahrain indicates that Hyspoasines occupied the islands, (and it also mention his wife, Thalassia). From the third century BC to the arrival of Islam in the seventh century AD, Bahrain was controlled by two other Iranian dynasties; the Parthians and Sassanids.

By about 250 BC, the Seleucids lost their territories to Parthians, an Iranian tribe from Central Asia. The Parthian dynasty brought the Persian Gulf under their control and extended their influence as far as Oman. Because they needed to control the Persian Gulf trade route, the Parthians established garrisons in the southern coast of the Persian Gulf.[18]

Asia in 600 CE, showing the Sassanid Empire before the Arab conquest.

In the third century AD, the Sassanids succeeded the Parthians and held the area until the rise of Islam, four centuries later.[18]Ardashir, the first ruler of the Sassanian dynasty marched forward to Oman and Bahrain and defeat Sanatruq[19] (or Satiran[2]), probably the Parthian governor of Bahrain.[20] He appointed his son Shapur I as governor of Bahrain. Shapur constructed a new city there and named it Batan Ardashir after his father.[2] At this time, Bahrain was incorporated into the southern Sassanid province covering the Persian Gulf's southern shore, plus the archipelago of Bahrain.[20] This southern province was subdivided into three districts of Haggar (now al-Hafuf province, Saudi Arabia), Batan Ardashir (now al-Qatif province, Saudi Arabia), and Mishmahig (now Bahrain Island)[2] (in Middle Persian/Pahlavi means "ewe-fish".[21]) included the Bahrain archipelago which was earlier called Aval, but later, in the Islamic era, became known as Bahrain.[2][20] The name 'ewe-fish' would appear to suggest that the name /Tulos/ is related to Hebrew /ṭāleh/ 'lamb' (Strong's 2924).[22]

By the fifth century Bahrain was a centre for Nestorian Christianity, with Samahij[23] the seat of bishops. In 410, according to the Oriental Syriac Church synodal records, a bishop named Batai was excommunicated from the church in Bahrain.[10] It was also the site of worship of a shark deity called Awal. Worshipers reputedly built a large statue to Awal in Muharraq, although it has now been lost, and for many centuries after Tylos, the islands of Bahrain were known as Awal.